Esters of phosphorus-oxygen acids, these esters comprising alkoxy groups, and their use as corrosion inhibitors and flameproofing agents

ABSTRACT

The invention relates to esters or ester salts of phosphorus-oxygen acids, these esters or ester salts comprising alkoxy groups, and to the use of compounds of this type as corrosion inhibitors, particularly in alkaline media, and as flameproofing agents.

The present invention relates to alkoxy-comprising esters or ester saltsof phosphorus-oxygen acids. It furthermore relates to the use of suchcompounds as corrosion inhibitors, in particular in alkaline medium.

The use of phosphoric or phosphonic acid derivatives for corrosionprotection is known in principle. Frequently, however, phosphoric orphosphonic acid derivatives or the hydrolysis products thereof forminsoluble or sparingly soluble salts with various opposite ions, e.g.Ca²⁺, in aqueous alkaline media, so that they can be used only to alimited extent in such media.

An alkaline medium may be, for example, concrete, mortar and the like orfinishes, coating systems or the like containing an alkaline bindersystem.

Steel reinforcements embedded in concrete are also not completelyprotected from corrosion but may corrode in the course of time. As aresult of the corrosion of the steel reinforcement, the strength thereofand hence the strength of the concrete are reduced. Moreover, thecorrosion products, for example iron oxides or hydrated iron oxides,have a larger volume than the uncorroded steel itself. Accordingly,stresses form in the concrete that can lead to cracks or to breaking offof whole fragments. Considerable economic damage is caused by corrosionof reinforced concrete.

The corrosion of the steel reinforcement is a substantiallydiffusion-controlled process. Water and oxygen can diffuse into thepores of the concrete. Pore water comprises, inter alia, dissolvedCa(OH)₂ and has, in intact concrete, a pH of about 13. At this pH, steelreinforcements embedded in concrete are protected from corrosion by apassivation layer. The diffusion of atmospheric CO₂ in the poresresults, inter alia, in the formation of insoluble CaCO₃ and the pH ofthe pore water falls to values below 9. However, at these pH values, thepassivation layer on the steel becomes ineffective. The effect of thepassivation layer can also be adversely affected or eliminated bychloride ions. Chloride ions can penetrate into the concrete, forexample through contact of the concrete with sea water or deicingcompositions.

The amount of penetrating CO₂ or chloride is smaller when particularlydense, concrete having few pores is used. However, the penetrationcannot be completely prevented in this way either. Moreover, when thestructure of the concrete changes, so do its properties, which isfrequently undesirable depending on the intended use. The possibility ofusing concrete having few pores is therefore not feasible in many cases.

It is therefore known that corrosion inhibitors, for example nitrites,amines, alkanolamines, mixtures thereof with inorganic or organic acidsor phosphate esters, can be added to fresh concrete. It is also knownthat phosphonic acids or phosphonic acid derivatives can be used forcorrosion protection in concrete. DE-A 36 29 234 discloses the additionof salts, in particular sodium salts of various alkylphosphonic acids,as an additive to concrete and mortar mixtures. GB-A 2 248 612 andJP-A-03-159945 disclose amino- or hydroxyl-containing phosphonic acidsas an additive for concrete.

In addition to the corrosion-protecting treatment of fresh concrete, thequestion regarding the protection of old concrete frequently arises inpractice. For this purpose, the concrete can be chipped off or blastedoff on the surface and the steel reinforcement exposed. The steelreinforcement can then be treated with corrosion inhibitors and finallycovered again with concrete. This method is used especially in seriouscases if the structure of the concrete is already irreversibly damaged.

It is furthermore known that the surface of hardened reinforced concretecan be treated with a migrating corrosion inhibitor. This technique isdisclosed, for example, in “M. Haynes, B. Malric, Construction Repair,July/August 1997” or in U.S. Pat. No. 5,071,579. For this purpose, asolution of the inhibitor is applied or sprayed several times insuccession on the surface, the inhibitor migrating into the surface. Thefurther diffusion into the interior down to the steel reinforcement isusually supported by the repeated application of water to the surface.It is known that Na₂PO₃F can be used as a migrating corrosion inhibitor.U.S. Pat. No. 5,071,579 also discloses the combined use of Na₂PO₃Ftogether with a phosphonic acid of the formulaR_(n)R_(l)N(CH₂PO₃H₂)_(2-n) (n=0 or 1). However, sodium fluorophosphateis hydrolyzed in water and forms insoluble calcium salts with Ca(OH)₂dissolved in the pore water. Phosphonic acids, too, form insolublecalcium salts. A considerable part of the superficially appliedcorrosion inhibitors thus does not reach the steel reinforcement at alland accordingly also cannot display any action. The inhibitors musttherefore be used in large amounts. This is uneconomical and moreoverthe concrete is contaminated by undesired components as a result.

It is an object of the present invention to provide improved corrosioninhibitors which are particularly suitable for use in an alkaline mediumand which in particular form no insoluble or sparingly soluble calciumsalts.

We have found that this object is achieved by alkoxy-comprising estersof phosphorus-oxygen acids of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OR²)]_(m)   (A)or[(R¹O)(R²O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)(OR²)]_(m)   (B)where

-   -   n is an integer from 0 to 10,    -   m+k=2 and m is 1 or 2 and k is 0 or 1,    -   at least one of the radicals R¹, R² and, if appropriate, R³ is        alkoxy of the formula —[CH₂—CHR⁶—O]_(l)R⁷, where l is from 2 to        30 and R⁶ and R⁷ are each H or CH₃,    -   and, where they are not alkoxy groups, R¹and R² are        straight-chain or branched C₁- to C₆-alkyl,    -   and, where it is not an alkoxy group, R³ is straight-chain or        branched, unsubstituted or substituted C₁- to C₂₀-alkyl or aryl,    -   R⁴ is H or straight-chain or branched C₁- to C₆-alkyl and    -   R⁵ is a divalent bridging group.

In a second aspect of the present invention, alkoxy-comprising estersalts of phosphorus-oxygen acids of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (C)or[(MO)(R¹O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—[—(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (D)were found, where

-   -   n is an integer from 0 to 10,    -   m+k=2 and m is 1 or 2 and k is 0 or 1,    -   at least one of the radicals R¹ and, if appropriate, R³ is        alkoxy of the formula —[CH₂₋CHR⁶—O]_(l)R⁷, where l is from 2 to        30 and R⁶ and R⁷ are each H or CH₃,    -   and, where it is not an alkoxy group, R¹ is straight-chain or        branched C₁- to C₆-alkyl,    -   and, where it is not an alkoxy group, R³ is straight-chain or        branched, unsubstituted or substituted C₁- to C₂₀-alkyl or aryl,    -   R⁴ is H or straight-chain or branched C₁- to C₆-alkyl and    -   R⁵ is a divalent bridging group, and    -   M is at least one cation selected from the group consisting of        alkali metal, alkaline earth metal or ammonium ions.

We have furthermore found the use of the esters or ester salts ascorrosion inhibitors, in particular migrating corrosion inhibitors forreinforced concrete.

Surprisingly, we have found that the novel diesters—what is meant is thenumber of ester groups per phosphorus atom—are very useful for corrosionprotection. They are very particularly suitable for an alkaline medium,if appropriate media comprising calcium ions. The novel esters aresoluble in saturated Ca(OH)₂ solution and form no sparingly solubleprecipitates. Furthermore, the solubility of the monoester salts inCa(OH)₂ solution is sufficient.

Even in an excess of NaOH and at elevated temperature, the diestershydrolyze in an alkaline medium in general only very slowly to give thecorresponding monoester salts. The further hydrolysis to give the freeacids or the salts thereof takes place only to a minor extent under saidconditions. The diesters themselves have a corrosion-inhibiting action.As a rule, the corrosion-inhibiting action of the correspondingmonoester salts is higher. The monoester salts are liberated onlygradually by hydrolysis. The diesters are masked corrosion inhibitors orcorrosion inhibitors having a delayed or long-term action.

Regarding the invention, the following may be stated specifically.

The novel, alkoxy-comprising esters of phosphorus-oxygen acids areeither diesters of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OR²)]_(m),   (A)in which one or two phosphorus-oxygen acid groups and at least onefurther substituent are linked directly or indirectly to a nitrogenatom, or a bridged diester of the formula[(R¹O)(R²O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)(OR²)]_(m),   (B)in which two nitrogen atoms are linked to one another via a group R⁵ andin turn have one or two phosphorus-oxygen acid groups and, ifappropriate, a further substituent.

Below, the term “diester” is intended to relate to the number of estergroups per phosphorus atom and hence denote compounds in which allphosphorus atoms present in the molecule have two ester groups each.Accordingly, the term “monoester” below is intended to denote compoundsin which each phosphorus atom has an ester group or an OH or OM group.The novel diesters or monoesters are a phosphonic acid derivative wheren is greater than 0, whereas they are a derivative of amidophosphoricacid where n is 0.

The index n in the formulae (A) and (B) is an integer from 0 to 10.Preferably, n is an integer from 0 to 3, particularly preferably 0 or 1,very particularly preferably 1.

The index m is 1 or 2 and the index k is 0 or 1, the sum of m+k being 2.Preferably, m and k are each 1, i.e. in each case only one—(CH₂)_(n)—PO(OR¹)(OR²) group is linked to a nitrogen atom.

At least one of the radicals R¹, R² and, if appropriate, R³ (i.e. wherethe diester is compound (A)) is alkoxy. Suitable alkoxy groups are inparticular polyoxyethylene or polyoxypropylene groups of the formula—[CH₂—CHR⁶—O]_(l)R⁷, where l is from 2 to 30 and R⁶ is H and/or CH₃. R⁵is preferably H, i.e. the alkoxy group is a polyoxyethylene group.Preferably, l is from 3 to 20, particularly preferably from 5 to 15. R⁷is a CH group or H.

It is known to a person skilled in the art that such alkoxy groups areobtainable, for example, by oxyalkylation or starting from industrialpolyglycols. Said values for l are thus average chain lengths, where theaverage value need not of course be a natural number but may also be anydesired rational number.

The remaining radical or radicals R¹, R² and, if appropriate, R³ (onlyfor case (A)) which is or are not alkoxy is or are straight-chain orbranched, unsubstituted or substituted alkyl. Optionally presentsubstituents may be, for example, amino or OH. In particular, thesubstituents may be a terminal OH group.

R¹ and/or R² is/are preferably C₁- to C₆-alkyl, for example methyl,ethyl, n-propyl, isopropyl, n-butyl, n-pentyl or n-hexyl, preferablymethyl or ethyl, very particularly preferably ethyl. A substituted alkylgroup may be in particular 2-methoxyethyl.

R³ is preferably C₁- to C₂₀-alkyl or aryl. It is preferablystraight-chain or branched C₄- to C₁₂-alkyl. Examples of suitable groupscomprise methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,n-pentyl, n-hexyl, 2-ethylhexyl, n-heptyl, n-octyl, n-nonyl, n-decyl orn-dodecyl. Particularly preferred groups comprise n-propyl, n-butyl,n-octyl and 2-ethylhexyl. A substituted alkyl group may be in particularan ω-methoxyalkyl group, e.g. methoxyethyl. Aryl groups may be pure arylgroups, such as alkyl-substituted aryl groups, for example a —CH₂C₅H₆group.

If present, R⁴ is H or straight-chain or branched, unsubstituted orsubstituted alkyl, preferably C₁- to C₆-alkyl. Particularly preferably,R⁴ is H or methyl. A substituted alkyl group may be in particular2-methoxyethyl.

No R³ is present in the bridged compound (B), but instead a divalentbridging group R⁵ which preferably has at least 2 carbon atoms. Saidgroup may be in particular a group derived from aliphatic, alicyclic oraromatic hydrocarbons. Examples comprise 1,4-xylylene, 1,4-cyclohexyleneor ethylidene groups which may also have heteroatoms or substituents.

The bridging group is preferably alkylene of 2 to 20 carbon atoms, inwhich nonneighboring CH₂ groups may also be substituted by O or N atoms.Examples comprise —(CH₂)₂—, —(CH₂)₄—, —(CH₂)₆—, —(CH₂)₈—,—(CH₂)₂—O—(CH₂)₂—, —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—,—(CH₂)₃—O—(CH₂)₄—O—(CH₂)₃—, —(CH₂)₃—O—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₃—,—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—,—(CH₂)₂—O—[(CH₂)₂—O—]_(j)(CH₂)₂—O—(CH₂)₂—, —(CH₂)₂—N—(CH₂)₂— and—(CH₂)₂—NR₆—(CH₂)₂—NR₆—(CH₂)₂— groups, where j is from 1 to 10 and R₆ isalkyl, —(CH₂)_(n)—PO(OR¹)(OR²) or —(CH₂)_(n)—PO(OR¹)(OM).

Said groups are preferably —(CH₂)₂—, —(CH₂)₄—, —(CH₂)₆—,—(CH₂)₃—O—(CH₂)₄—O—(CH₂)₃—, —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂— or—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂— groups.

Among the various possible combinations of the radicals R¹ to R⁷, aperson skilled in the art makes a suitable choice according to thedesired properties and the intended use. For carrying out the invention,it is sufficient if one of the radicals R¹ and R² is alkoxy. Preferably,however, both R¹ and R² are alkoxy.

Migrating corrosion inhibitors which have proven particularly useful arethe following compounds:

(2-ethylhexyl)-N(CH₃)—(CH₂)—PO(O-alkoxy)(O-alkoxy),

(2-ethylhexyl)-N[—(CH₂)—PO(O-alkoxy)(O-alkoxy)]₂,

butyl-NH—PO(O-alkoxy)(O-alkoxy),

octyl-NH—PO(O-alkoxy)(O-alkoxy),

(2-ethylhexyl)-NH—PO(O-alkoxy)(O-alkoxy),

(2-ethylhexyl)-N(CH₃)—PO(O-alkoxy)(O-alkoxy),

(alkoxy)-NH—PO(O-alkoxy)(O-alkoxy),

(alkoxy-O)(alkoxy-O)OP—NH—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—NH—PO(O-alkoxy)(O-alkoxy)

(2-methoxyethyl)₂N—CH₂—PO(O-alkoxy)(O-alkoxy),

(ethyl)₂N—CH₂—PO(O-alkoxy)(O-alkoxy),

(CH₂)₅N—CH₂—PO(O-alkoxy)(O-alkoxy),

In the novel ester saltsR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (C)and[(MO)(R¹O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)OM)]_(m)   (D)the radicals—if present—and indices have the meaning stated above in thedescription of the diesters. However, the ester salts have only oneester group per phosphorus atom. In the case of (D), R¹ is alwaysalkoxy; in the case of (C), either R¹ or R³ may be alkoxy, or R¹ and R³together.

M is at least one cation selected from the group consisting of alkalimetal, alkaline earth metal or ammonium ions. The ammonium ions may bein particular NH₄ ⁺, alkyl- or hydroxyalkyl-substituted ammonium ions,for example (HOCH₂CH₂)₃NH⁺, (HOCH₂CH₂)₂NH₂ ⁺, HOCH₂CH₂NH₃ ⁺ orHOCH₂CH₂N(CH₃)₂H⁺, or else tetraalkylammonium ions, for exampletetramethylammonium or tetraethylammonium. Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, Ce⁺⁺⁺,Al⁺⁺⁺, Zn⁺⁺ and NH₄ ⁺ are preferred. The above formulae represent onlythe case of monovalent cations for the sake of simplicity. A personskilled in the art can, however, readily derive therefrom the correctformulae for polyvalent cations.

The novel diesters of phosphorus-oxygen acids can be prepared, forexample, starting from commercially available phosphonic esters, forexample diethyl phosphonate.

An alkoxylated diester can be obtained therefrom by transesterification,by reacting diethyl phosphonate with the polyethylene glycol orpolypropylene glycol desired in each case or the respective monoethers.The transesterification can be catalyzed, for example, by alkali metals,and ethanol liberated is distilled off.

It is of course also possible to start from phosphonic acid itself andto oxyalkylate it by methods known in principle to a person skilled inthe art. In this case, alkoxy groups which still have a terminal OHgroup are obtained.

For n=0, the dialkoxy esters obtained can be reacted with the desiredamine, for example ethylhexylamine. The reaction can be carried out in amanner known in principle in CCl₄ and a tertiary amine as a catalyst.The use of diamines, such as ethylenediamine, results in bridgeddiesters (B). The use of aminopolyethylene or polypropylene glycolresults in diesters which have an alkoxy group as R³.

Diesters in which n=1 can be obtained by aminomethylation of diethylphosphonate or of the corresponding alkoxylated diester. Here, thephosphonic diester is reacted with formaldehyde, the desired amine and asuitable Brönsted acid.

Diesters in which n=2 can be prepared by addition of amines tovinylphosphonic esters and, for n>2, by free-radical addition ofphosphonic diesters at double bonds (e.g. to allylamines for n=3) or theArbuzov reaction with aminoalkyl bromides.

The ester-salts are preferably prepared by alkaline hydrolysis of thediesters, for example by heating the diesters in aqueous NaOH totemperatures of from 60 to 100° C. for from 2 to 12 hours, substantiallyonly one ester group per phosphorus atom being hydrolyzed. The optimumconditions for the compound desired in each case can be determined by aperson skilled in the art, if appropriate by means of only a fewexperiments. The monoester salts can also be formed in situ, byhydrolysis in the medium of use.

The novel diesters and monoester salts can be used as corrosioninhibitors. They are particularly-suitable for use in alkaline media,for example having a pH of from 8 to 13. They are furthermoreparticularly suitable for use in the presence of Ca²⁺ ions.

The novel diesters and monoester salts can be used as such for corrosionprotection. For example, suitable derivatives can be sprayed or pouredonto a metallic surface, if appropriate after gentle heating. They canalso be added to other substances or mixtures, for example finishes,printing inks, mortar or concrete and can thus prevent corrosion oncontact of said substances or mixtures with metals.

However, the diesters and monoester salts are preferably used in theform of suitable formulations which comprise at least one diester and/orone monoester salt, a suitable solvent and optionally furthercomponents.

Suitable solvents are in particular water or alcohols, such as methanol,ethanol, propanol, polyethylene glycol or alkylpolyethylene glycols. Itis of course also possible to use mixtures of different solvents.

Formulations which comprise a predominantly aqueous solvent mixture arepreferred. This is to be understood as meaning mixtures which compriseat least 50, preferably at least 65, particularly preferably at least80, % by weight of water. Further components are water-misciblesolvents. Examples comprise monoalcohols, such as methanol, ethanol orpropanol, higher alcohols, such as ethylene glycol, glycerol orpolyetherpolyols, and ether alcohols, such as butylglycol ormethoxypropanol.

Depending on the type of corrosion inhibitor used and on the desireduse, a person skilled in the art makes a suitable choice from among thesolvents possible in principle.

A particularly preferred solvent is water.

The pH of the formulation is chosen by a person skilled in the artaccording to the desired use. The use of corrosion inhibitors in anaqueous alkaline medium, for example at a pH of from 8 to 13, ispreferred.

The concentration of the corrosion inhibitors is established by a personskilled in the art according to the desired purpose. It is of coursealso possible to prepare concentrates, which are not diluted to thedesired concentration until before the actual use on site.

It is also possible to use further corrosion inhibitors as a mixturewith the novel inhibitors, provided that no disadvantageous effectsoccur.

The formulations comprising the novel corrosion inhibitors are appliedin a suitable manner, for example by coating, spraying, printing orimmersion, to the metal surface to be protected. The metal surfaces maybe in general industrially customary materials selected from the groupconsisting of aluminum alloys and magnesium alloys, iron, steel, copper,zinc, tin, nickel, chromium and industrially customary alloys of thesemetals. Further examples comprise industrially customary metal coatingswhich may be produced by chemical or electrochemical methods, selectedfrom the group consisting of zinc and its alloys, preferably metalliczinc, zinc/iron, zinc/nickel, zinc/manganese or zinc/cobalt alloys, tinand its alloys, preferably metallic tin, alloys of tin which compriseCu, Sb, Pb, Ag, Bi and Zn, particularly preferably those which are usedas solders, for example in the production and processing of circuitboards, and copper, preferably in the form in which it is used oncircuit boards and metallized plastics parts.

The metal surfaces to be protected may also be metal particles or metallamellae, for example aluminum flakes. Such metal effect pigments areused for a very wide range of purposes, depending on particle size.Relatively small particles are used as silver bronzes, for example inprinting inks or finishes, while relatively large particles serve ascorrosion protection pigments in finishes. The novel diesters andmonoester salts can be added to the printing inks or finishes, or elsethe metal effect pigments are treated with a novel formulation prior toincorporation.

The novel diesters and monoester salts are particularly suitable forcorrosion protection of reinforced concrete. On the one hand, they canbe added to the fresh concrete. They can also be used for the renovationof old concrete, for example for the treatment of exposed steelreinforcement. They are also suitable as migrating corrosion inhibitors.

The novel compounds can of course also be used in other areas. They arealso suitable, for example, as flameproofing agents.

The examples which follow illustrate the invention in more detail:

Starting Materials Used:

Pluriol® A 275E: methylpolyethylene glycol ether, M_(w) 275 g/mol (BASFAG).

In the examples, the compound is referred to as methoxyhexaethyleneglycol for the sake of simplicity. In fact, it is a mixture of variousmethylpolyethylene glycols having a mean value of 5.5 with a number of—CH₂CH₂O— units present.

For the experiments, it is also possible to use other methylpolyethyleneglycol ethers having other average molecular weights M_(w), e.g.Pluriol® A 350E (M_(w) 350 g/mol) or Pluriol® A 500E (M_(w) 500 g/mol).

EXAMPLE 1 Preparation of di(methylhexaethylene glycol) phosphite

Diethyl phosphite (12.8 g, 0.093 mol) and Pluriol A 275 E (50 g, 0.186mol) are initially taken together in a 500 ml flask. After the additionof potassium (20 mg, 0.5 mmol) as a catalyst, the reaction mixture isheated to 170° C. and EtOH formed is distilled off under atmosphericpressure. The remaining EtOH is evaporated at 20 mmHg. The yield is95-98%.

By using other polyethylene glycol ethers having a higher or lowermolecular weight, phosphonic esters having other ester groups can beobtained.

In an alternative method of preparation, di(methylhexaethylene glycol)phosphite is also prepared by direct ethoxylation of phosphonic acid.

EXAMPLE 2 Preparation of 2-ethylhexylphosphoramide di(methylhexaethyleneglycol) ester

62.0 g (0.092 mol) of the di(methylhexaethylene glycol) phosphiteobtained according to example 1 are dissolved in a 1:1 CCl₄/CH₂Cl₂ (185ml) mixture, and 2-ethylhexylamine (11.9 g, 0.092 mol) is added (R³ inthe above formula is 2-ethylhexyl). Finally, triethylamine (9.28 g,0.092 mol) is added dropwise. The white triethylammonium hydrochloridepowder is filtered off and the solvent is distilled off.2-Ethylhexylphosphoramide di(methylhexaethylene glycol) ester isobtained as a transparent liquid in a yield of 76% (based on synthesismethod of F. R. Atherton, A. R. Todd, J. Am. Chem. Soc., (1947), 674,ibid. (1945), 660).

Other compounds obtainable according to the method of example 1 can alsobe used as the phosphonic ester. Instead of 2-ethylhexylamine, otheramines can also be used.

EXAMPLE 3 Preparation of di(methylhexaethylene glycol)N-methyl-N-2-ethylhexylaminomethyl-phosphite

Di(methylhexaethylene glycol) phosphite (0.1 mol) is added dropwise inthe course of 1 hour to a mixture of N-methyl-2-ethylhexylamine (14.3 g,0.1 mol), formaldehyde (8.21 g, 36.5% strength solution, 0.1 mol) ando-phosphoric acid (4.89 g, 85% strength, 5% by weight) while cooling at−11° C. Thereafter, the reaction mixture is heated to 90° C. and kept atthis temperature for 3 hours.

Instead of the o-phosphoric acid, it is also possible to use an acidicion exchanger, for example Amberlyst 36Dry, in an amount of 1% byweight, based on the total amount, as a catalyst. Other compoundsobtainable according to example 1 may also be used as the phosphonicester. Instead of 2-ethylhexylamine, other amines may also be used. Withthe use of primary amines, the corresponding dimer is also formed inaddition to the above product. This is shown below by way of example forthe use of octylamine.

EXAMPLE 4 Preparation of di(hydroxyhexaethylene glycol)N-methyl-N-2-ethylhexylaminomethyl-phosphite

1st Stage: Synthesis of the Phosphonic Acid

The phosphonic acid A is synthesized in a first reaction stage on thebasis of the synthesis method of K. Moedritzer, R. R. Irani, J. Org.Chem. (1966), 1603-1607, according to the above equation.

2nd Stage: Ethoxylation of the Phosphonic Acid

N-Methyl-N-2-ethylhexylaminomethylphosphonic acid (238 g, 1 mol) issuspended in 2 l of toluene, and 14 equivalents of ethylene oxide (616g, 14 mol) are slowly metered in at 50° C. and 1-1.5 bar. The solvent isseparated from the product (B) under reduced pressure.

General Method for Hydrolysis of the Diesters to Give the Monoesters

Di(methylpolyethylene glycol) dialkylaminomethylphosphites oralkylphosphoramide di(methylpolyethylene glycol) esters (0.05 mol) areinitially taken in a 100 ml four-necked flask having a thermocouple,temperature regulator, coil condenser and bubble counter. The product isdiluted with demineralized water (37.0 g). Sodium hydroxide solution(50%, 8 g, 0.1 mol) is then added dropwise in the course of about 10minutes, the temperature increasing to not more than 32° C. Aftercomplete addition, heating is effected slowly to a reflux temperature of100-105° C. and the reaction mixture is kept at this temperature for 8hours. The product is characterized by ³¹P, ¹H and ¹³C-NMR.

Under these conditions, only monohydrolysis product can be detected.

Use of the novel compounds as a corrosion inhibitor in an alkalinemedium:

General Working Method:

The metal test sheets (2 cm×5 cm, steel 1.0037) are pretreated bycathodic alkaline degreasing and subsequent electrolytic derusting.

The samples are covered with a test solution for 7 days and the loss ofmass of the metal test sheet is then determined. The correspondingcorrosion inhibitor is added to the test solutions. A comparativeexperiment is carried out in each case using the same metal sheet andthe same test solution but without addition of the corrosion inhibitor.

The corrosion protection efficiency is obtained by comparison of theloss of mass of the metal sheet tested with and without corrosioninhibitor.Efficiency [%]=[(ΔM ₀ −ΔM)/(ΔM ₀)]·100.

ΔM₀: Loss of mass of the metal sheet without corrosion inhibitor

ΔM: Loss of mass of the metal sheet with addition of corrosioninhibitor.

Test solution: Demineralized water, 0.03 mol/l NaCl, brought to pH 10with KOH

Concentration of the corrosion inhibitor in the solution: 1% by weightin each case.

Table 1 shows the corrosion protection efficiency of different novelcorrosion inhibitors. A zero sample and a sample containing theconventional corrosion inhibitor monoethanolamine are also run ascomparative experiments.

Behavior of the Novel Corrosion Inhibitors in Concrete:

General Working Method:

For testing the migration behavior of the novel corrosion inhibitors,concrete sheets 75 mm long, 20 mm wide and 4 mm thick are used. As inthe case of thin-layer chromatography, the concrete sheets are placedperpendicularly in a test solution comprising in each case 10% by weightof the novel corrosion inhibitors in water so that they dip about 1 cminto the solution at the lower edge. In order to prevent evaporation ofthe test solution, the tests are carried out in a closed vessel, forexample a glass jar of suitable size which has a snap-on cover. After 1day, the test solution has migrated upward to the upper edge of thesheet.

For analysis, a sample is broken off from the upper third of theconcrete sheet after one day and is ground, and the phosphorus contentis analyzed. The phosphorus content of an untreated concrete sheet wassubtracted in each case.

Experiments with 3 different novel compounds were carried out. Theresults are listed in table 2 and show that the novel compounds havegood migration behavior. TABLE 1 Efficiency of the novel corrosioninhibitors in an alkaline medium Hydrolyzed to the Corrosion inhibitormonoester Efficiency No. (concentration in each case 1% by weight) saltFormula [%] Example 5 Product of di (2-methoxyethyl)amine, formaldehydeand di(methylhexaethylene glycol) phosphite (according to example 3) Yes

65 Example 6 As for example 5 No

30 Example 7 Product of octylamine and di(methylhexaethylene glycol)phosphite (according to example 2) Yes

92 Example 8 Product of butylamine and di(methylhexaethylene glycol)phosphite (according to example 2) Yes

73 Example 9 Product of N-methyl-2-ethylhexylamine anddi(methylhexaethylene glycol) phosphite (according to example 2) Yes

75 Example 10 As for example 9 No

39 Comp. No inhibitor — 0 example 1 Comp. Monoethanolamine inhibitorHO—CH₂—CH₂—NH₂ 10 example 2

TABLE 2 P analyses after carrying out migration test in concrete Pcontent No. Corrosion inhibitor Formula [mg/100 g] Example 11 Product ofdi(2-methoxyethyl)amine, formaldehyde and di(methylhexaethylene glycol)phosphite

55 Example 12 As for example 11, partly hydrolyzed with NaOH

52 Example 13 Product of butylamine and di(methylpolyethylene glycol)phosphite

40

1. A corrosion inhibitor which comprises an alkoxy-comprising ester ofphosphorus-oxygen acids of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OR²)]_(m)   (A)or[(R¹O)(R²O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)(OR²)]_(m)   (B) and/or analkoxy-comprisingester salt of phosphorus-oxygen acids of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (C)or[(MO)(R¹O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (D) where n is an integer from 0 to10, m+k=2 and m is 1 or 2 and k is 0 or 1, at least one of the radicalsR¹, R² and, if appropriate, R³ is alkoxy of the formula—[CH₂—CHR⁶—O]_(l)R⁷, where l is from 2 to 30 and R⁶ and R⁷ are each H orCH₃, and, where, they are not alkoxy groups, R¹ and R² arestraight-chain or branched, unsubstituted or substituted C₁- toC₆-alkyl, and, where it is not an alkoxy group, R³ is straight-chain orbranched, unsubstituted or substituted C₁- to C₂₀-alkyl or aryl, R⁴ is Hor straight-chain or branched, unsubstituted or substituted C₁- toC₆-alkyl R⁵ is a divalent bridging group, and M is at least one cationselected from the group consisting of alkali metal, alkaline earth metalor amnionium ions.
 2. The inhibitor according to claim 1, wherein thecorrosion inhibitor is used in an alkaline medium.
 3. The inhibitoraccording to claim 1, wherein the medium is an aqueous medium.
 4. Theinhibitor according to claim 1, wherein n is 0 or
 1. 5. The inhibitoraccording to claim 1, wherein k and m are each
 1. 6. The inhibitoraccording to claim 1, wherein l is from 3 to
 20. 7. The inhibitoraccording to claim 1, wherein R⁶ is H.
 8. An alkoxy-comprising estersalt of phosphorus-oxygen acids of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (C)or[(MO)(R¹O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)(OM)]_(m)   (D) where n is an integer from 0 to10, m+k=2 and m is 1 or 2 and k is 0 or 1, at least one of the radicalsR¹ and, if appropriate, R³ is alkoxy of the formula —[CH₂—CHR⁶—O]_(l)R⁷,where l is from 2 to 30 and R⁶ and R⁷ are each H or CH₃, and, where itis not an alkoxy group, R¹ is straight-chain or branched, unsubstitutedor substituted C₁- to C₆-alkyl, and, where it is not an alkoxy group, R³is straight-chain or branched, unsubstituted or substituted C₁- toC₂₀-alkyl or aryl, R⁴ is H or straight-chain or branched, unsubstitutedor substituted C₁- to C₆-alkyl and R⁵ is a divalent bridging group, andM is at least one cation selected from the group consisting of alkalimetal, alkaline earth metal or ammonium ions.
 9. An alkoxy-comprisingester of phosphorus-oxygen acids of the formulaR³—NR⁴ _(k)—[(CH₂)_(n)—PO(OR¹)(OR²)]_(m)   (A)or[(R¹O)(R²O)OP—(CH₂)_(n)—]_(m)—NR⁴ _(k)—R⁵—NR⁴_(k)—[—(CH₂)_(n)—PO(OR¹)(OR²)]_(m)   (B) where n is an integer from 0 to10, m+k=2 and m is 1 or 2 and k is 0 or 1, least one of the radicals R¹,R² and, if appropriate, R³ is alkoxy of the formula —[CH₂—CHR⁶—O]_(l)CH₃where l is from 2 to 30 and R⁶ is H or CH₃, and, where they are notalkoxy groups, R¹ and R² are straight-chain or branched, unsubstitutedor substituted C₁- to C₆-alkyl, and, where it is not an alkoxy group, R³is straight-chain or branched, unsubstituted or substituted C₁- toC₂₀-alkyl or aryl, R⁴ is H or straight-chain or branched, unsubstitutedor substituted C₁- to C₆-alkyl and R⁵ is a divalent bridging group. 10.The inhibitor according to claim 2, wherein n is 0 or
 1. 11. Theinhibitor according to claim 10, wherein k and m are each
 1. 12. Theinhibitor according to claim 11, wherein l is from 3 to
 20. 13. Theinhibitor according to claim 12, wherein R⁶ is H.
 14. The inhibitoraccording to claim 11, wherein l is from 5 to 15 and n is
 1. 15. Theinhibitor according to claim 1, wherein R¹ or R² is 2-methoxyethyl. 16.The inhibitor according to claim 1, wherein R⁴ is H, methyl or2-methoxyethyl.
 17. The alkoxy according to claim 9, wherein R⁴ is H,methyl or 2-methoxyethyl.